If I start mining after maxing out my character's levels, I get a dialog just after the first blocks appear:
"You must complete some of your available challenges before you can get more. Purchase challenges at the Store. [Go To Store] [Keep Mining]"
The warning is misleading for players who have maxed out their levels, since there are no more challenges to purchase. But my main complaint is that the warning interrupts me and requires an extra tap. It would be better for the warning to be a non-modal part of the "begin mining" screen (the one with the difficulty slider), like this:
/!\ You have unlocked all of Aurora Feint's challenges, but you may continue mining for fun.